void marsaglia()
{
  
  using namespace std;
  gROOT->Reset();


  TFile* f = (TFile*)gROOT->FindObject("marsaglia.root"); if (f) f->Close();
  f = new TFile ("marsaglia.root","RECREATE","");

  TTree * t = new TTree("t", "Nuovo Tree");
  int a = 16807;
  int m = 2147483647;
  int c=0;   //generatore di tipo moltiplicativo
  int Nmax=10000;
  int z, i;

  double PI = 3.141592653;
  double u, u0, y, rsq, mar;
  	

	t->Branch("Marsaglia", &mar, "mar/D");

	int z0 = 12; //seme

	for(i=0; i< Nmax; i++){
	z = (a*z0 +c) % m ;
	u = (double)z/(double)m; 
	u0 = (double)z0/(double)m;
	rsq = u*u + u0*u0;
        if(rsq <= 1){
	    mar = sqrt(-2*log(rsq)/rsq)*u;
	t->Fill();
	}

	z0 = z;
	}
	
  f->cd();
  t->Write();
  f->Close();
}